Electronic devices generate heat during operation. Thermal management refers to the ability to keep temperature-sensitive elements in an electronic device within a prescribed operating temperature. Thermal management has evolved to address the increased heat generation created within such electronic devices as a result of increased processing speed/power of the electronic devices.
Historically, electronic devices were cooled by a natural convection thermal management technique. The cases or packaging of these prior art electronic devices were designed with openings (e.g., slots) strategically located to allow warm air to escape and cooler air to be drawn in.
The processing speeds of computer systems have recently climbed from 25 MHZ to more than 1000 MHZ. The advent of such high performance processors and electronic devices now requires more innovative thermal management. Each of these increases in processing speed and power generally carries a “cost” of increased heat generation such that natural convection is no longer sufficient to provide proper thermal management.
Several methods have been employed for cooling high performance electronic devices such as processors. One common method of cooling these types of processors is by attaching heat sinks to a processor. The heat sinks are typically used in combination with a fan that forces air to pass by the heat sinks and/or processor.
There are several problems with cooling systems that utilize some form of a heat sink and fan combination. One problem is that the fan must typically be located too closely to the fins of the heat sink to generate fully developed air flow. When a large fan is used in conjunction with a heat sink to cool an electronic component, a large percentage of the air moved by the system fan does not go through the heat sink. As a result, even large fans are not an efficient thermal solution for cooling some electronic devices.
Some of the new high performance cooling systems are utilizing multiple fans to maintain proper operating temperatures. However, the additional fans in multiple fan cooling systems adds unwanted expense to manufacturing such electronic devices. In addition, the additional fans are noisy, bulky and utilize an inordinate amount of space within the environment where the electronic device is located.
An alternative and more costly system to manage the thermal energy output of high-powered processors is a “single-phase” pumped liquid cooling system. The system uses a heat exchanger that is thermally connected to the processor. The heat exchanger draws thermal energy from the processor and heats up a liquid coolant which is passed through the heat exchanger. A pump transfers the liquid coolant through a second heat exchanger that draws the thermal energy from the liquid coolant. The liquid coolant leaves the second heat exchanger at a low enough temperature to cool the processor once the coolant cycles back to the first heat exchanger.
These single-phase cooling systems suffer from several drawbacks. One drawback is that the systems are inefficient. Another drawback is that the systems require the use of a pump. These pumps require maintenance and commonly break down or leak onto one or more of the electrical components.
The most recent trend has seen the use of “two-phase” cooling systems to cool high-powered processors. These “two phase” cooling systems include an evaporator that removes thermal energy from the processor. The thermal energy causes a coolant within the evaporator to turn from a liquid into a vapor (i.e., to evaporate).
The coolant is typically transferred through an expansion valve before the coolant enters the evaporator. The expansion valve reduces the pressure of the coolant and also the temperature to enhance the efficiency of the cooling system and allow for coolant temperatures that are different than what otherwise would normally be available.
The coolant also typically exits the evaporator into a compressor, or pump, that transports the coolant from the evaporator into a condenser. The coolant leaves the pump at a higher pressure and temperature such that as the coolant flows through the condenser, energy can be easily removed from the coolant to the local air causing any vaporized coolant to readily condense back to a liquid. Once the coolant is in liquid form, it can be transported back to the evaporator after passing through the expansion valve.
These two-phase cooling systems also require the use of a pump such that they suffer from many of the drawbacks of single-phase systems. If these types of cooling systems are operated without using a pump, there could be problems depending on the orientation of the cooling system. In some orientations gravity forces the liquid coolant away from the evaporator making it impossible for the evaporator to cool the processor through evaporation of the coolant.
Since existing two-phase pumpless cooling systems do not effectively cool high performance processors under certain operating conditions, what is needed is a two-phase cooling system that provides high performance cooling under a variety of operating conditions for electronic components with high power generation.